1. Field of the Invention
This invention relates to dispensers for fluid products, and more particularly to a system for automatically filling a cup or container with a fluid product which may be highly viscous and which may have a density which varies in an unpredictable manner.
2. Description of the Prior Art
In restaurants, particularly of the fast food variety, it is particularly desirable to allow containers or cups to be automatically filled to predetermined levels. In this type establishment the individual serving a customer places the container beneath a dispensing outlet and manually initiates the filling of the container. Since the filling will automatically terminate at a predetermined level, the individual can then prepare the remaining portions of the customer's order while the container is being filled. Consequently, such automatic fill level systems can markedly increase the throughput capacity of such establishments.
Prior art automatic fill level dispensers typically operate in accordance with a number of separate principles. One operating principle is to merely allow the product to flow into the container for a predetermined period of time after which filling terminates. This technique is satisfactory for relatively low viscosity and constant viscosity products such as soft drinks which flow at a constant rate. However, the flow rate of highly viscous products and products having a variable viscosity such as milkshakes varies, thereby making this technique impractical.
A second technique for automatically filling a container to a predetermined level is to place the container on an automatic weighing device which terminates flow of the product to the container when the weight of the product within the container reaches a predetermined value. Once again, this technique is highly satisfactory for products having a constant density, but it is not practical for products such as milkshakes which have a variable density caused by such characteristics as the quantity of air in the product.
A third automatic filling technique utilizes optical sensors for determing when the product reaches a predetermined level in the container. Although this technique avoids problems inherent in the time duration filling technique and the weighing technique, it is usually not practical in fast food establishments since the containers are generally waxed paper cups which are somewhat opaque and which have a translucence which varies considerably.
A fourth variety of fluid level detector utilizes capacitive sensors which are either immersed in the fluid such as the systems disclosed in U.S. Pat. No. 3,746,975 issued to Alpby, U.S. Pat. No. 3,801,902 issued to Horowitz and U.S. Pat. No. 3,868,664 issued to Hill or they dispense the fluid into a specially constructed container such as the systems disclosed in U.S. Pat. No. 4,069,710 issued to Treier, U.S. Pat. No. 3,706,980 issued to Maltby and U.S. Pat. No. 4,002,996 issued to Klebanoff et al. Neither of these techniques are acceptable for use in a typical fast food establishment. When the product is milkshake, for example, the dispenser may dispense more than one flavor so that it would be necessary to clean immersible capacitance sensors after each container was filled. Furthermore, milkshake dropping from the sensor would make this approach unreasonably messy. The special container approach is also unacceptable because the containers used in a typical fast food establishment are normally discarded after use necessitating that the container be relatively inexpensive. Inexpensive containers do not have the highly controlled electrical parameters required by the special container approach.
For the reasons described above, an automatic fill level control system capable of handling such products as milkshakes is not commercially available. Consequently, even highly automated fast food establishments which utilize automatic fill level control systems for soft drinks must manually operate milkshake dispensing machines throughout the entire dispensing procedure. This results in a substantial limitation on the throughput capacity of such establishments.